It's not an efficient way to ship stuff. Wandering around a store picking an order takes much longer than an optimized warehouse.
Square footage is much more expensive retail than in a warehouse. So the area (if there's even room for it) where you pack and ship stuff costs more.
Shipping is more expensive because you are doing a few boxes a day instead of a semi-truck a day to UPS/FedEx/USPS
It just doesn't work that well. Fine as a stop gap for a small retailer dipping their toes in the online market. But for any sort of scale the warehouse model is much better.
I think the article is way off here. Yeah, some Sam's Clubs in the middle of nowhere were converted and a high end retailer has the margins to absorb the inefficiency. But the idea that existing retail is going to convert to warehouses at any sort of scale is laughable. The real estate costs are prohibitive and they'll end up somewhere an hour away where land is cheap.